Limited information on the prevalence of bacterial isolates associated with infections in pet guinea pigs is available. Historically, Streptococcus spp. has been reported as a common isolate. However, Corynebacterium spp., particularly Corynebacterium renale, has been seen frequently at the authors’ clinic, specifically in urinary tract infections. Corynebacterium renale is known for its role in bovine cystitis and pyelonephritis but has rarely been implicated in infections in guinea pigs. Therefore, the medical records of the University of Wisconsin-Madison Veterinary Teaching Hospital were searched for bacterial cultures performed in guinea pigs between 2004-2023. Sixty-two cases with growth on bacterial culture were identified. Streptococcus and Corynebacterium were the two most prevalent bacterial genera (26% of isolates and 24% of isolates respectively). The most common bacterial species was Corynebacterium renale (18% of all isolates) followed by Streptococcus equi (10% of all isolates). Corynebacterium was the most common genera isolated from the urinary tract (8/12 isolates, 67%) and Corynebacterium renale was the most prevalent species (7/12 isolates, 58%). Corynebacterium species were also isolated from an abscess (1/24 isolates, 4%), the nasal cavity (2/10 isolates, 20%), the vagina (1/2 isolates, 50%), and the cornea (2/3 isolates, 67%). Only 53% of Corynebacterium isolates were susceptible to trimethoprim-sulfamethoxazole (8/15 isolates), while 100% were susceptible to doxycycline. In conclusion, bacterial infections with Corynebacterium spp. appear more prevalent in pet guinea pigs than previously reported, with the majority of urinary tract pathogens isolated at this teaching hospital being Corynebacterium renale.